The present invention relates to packing and analogous machines in general, and more particularly to improvements in heat-treatment of wrappers in such machines.
The invention will be described with reference to the making of cigarette packs with the understanding, however, that the invention can be embodied with equal advantage in machines for the packing or sealing of other types of commodities. A cigarette packing machine is often equipped or associated with a discrete apparatus or comprises an integral unit which serves to provide cigarette packs with outer envelopes or wrappers consisting of a transparent or translucent material. The flaps, tucks or other projecting parts of such outer wrappers must be bonded to each other in order to prevent accidental opening of packs in storage or during shipment. As a rule, the packs are introduced into the pockets of a turret or another suitable transporting device and are moved stepwise to a sealing station where a heated sealing tool engages the adjacent flap or tuck of the thermoplastic outer wrapper and bonds it to the neighboring flap, tuck or another portion of such wrapper. The arrangement is such that the sealing tool is moved into engagement with successive outer wrappers during successive intervals of idleness of the transporting device.
A drawback of presently known packing machines which are equipped with such sealing tools is that the means for moving the sealing tool into and from engagement with successive heat-sealable outer wrappers receives motion from the main prime mover of the machine. The speed of such prime mover must be varied for a number of reasons. This presents problems in connection with retention of the sealing tool in engagement with successive outer wrappers for requisite intervals of time. Thus, when the main prime mover is driven at an elevated speed, the intervals of engagement between the sealing tool and successive outer wrappers are shortened and this can result in the making of unsatisfactory bonds. On the other hand, when the main prime mover is decelerated, it is likely to retain the sealing tool in prolonged heat-transmitting engagement with successive outer wrappers so that the material of such wrappers is or is likely to be discolored, charred or burned. The situation is analogous when a heated tool is brought into contact with successive cigarette packs, cigarettes or other commodities for the sole purpose of rapidly expelling moisture from adhesive bonds, e.g., from seams between overlapping marginal portions of webs of cigarette paper, tipping paper or the like. In other words, the effective heating, sealing or drying time depends on the momentary speed of the main prime mover of the machine with attendant problems when the speed is increased or reduced to such an extent that the intervals of engagement between the heated tool and successive commodities are too short or too long. Since the speed of the main prime mover does vary, a certain number of commodities cannot be treated to an optimum extent because the intervals of engagement between the heat-transmitting tool and successive commodities are directly dependent upon the speed of the main prime mover. The speed of the main prime mover is normally less than the nominal (optimum) speed immediately after starting as well as when the machine is to be inspected for the purpose of detecting flaws in the operation of one or more components, such as the transporting device or devices for cigarette packs, wrapping paper, labels and/or other constituents of cigarette packs. At such times, the actual speed of the main prime mover is normally only half the nominal speed.
German Offenlegungsschrift No. 1,965,693 discloses an apparatus wherein the intervals of engagement between a heat-transmitting tool and successive commodities are regulated by a time-delay element which can control the flow of a fluid to a cylinder serving to adjust a lever which carries the tool. The apparatus of this German publication is intended for the making of plastic bags or similar receptacles. Its main drawback is that it cannot control the movements of the tool with requisite accuracy when the tool must be moved to or from its operative position as often as five-hundred times per minute, a requirement which must be met in a modern high-speed cigarette packing machine.